In general, in the case of a steering wheel, a fuel gauge, and various mechanical devices, it is important to measure an accurate value of a rotation angle so as to perform precise control. Therefore, an angle sensor is used to measure the rotation angle of a rotating object.
The angle sensor utilizes a technique of emitting and receiving light or a technique of using inductance of a coil.
As shown in FIG. 1, a conventional inductive angle sensor is configured by arranging a semicircular coupler 4 over an exciting coil 2 wound in a ring shape with a pair of receiver coils 6 and 8 interposed therebetween.
The first receiver coil 6 is used to obtain information on the rotation angle using a differential signal that varies when the coupler 4 rotates. The second receiver coil 8 is used to obtain information on the distance between the coupler 4 and a sensor substrate using a differential signal that varies according to a change in distance from the coupler 4.
Since the conventional inductive angle sensor uses the pair of receiver coils 6 and 8, at least two substrates are required, and thus the overall structure is complicated.
Moreover, as shown in FIG. 2, in the case of the conventional inductive angle sensor, a signal processor 10 is connected to the sensor to process the information (signals) obtained from the receiver coils 6 and 8, thus extracting necessary information.
The signal process performed by the signal processor 10 will be described below.
First, when an oscillation voltage Vosc, expressed by the following Math Figure 1, is applied from an oscillator connected to the exciting coil 2, a first received voltage Ax and a second received voltage Bx, expressed by the following Math Figures 2 and 3, are obtained from the first and second receiver coils 6 and 8.MathFigure 1Vosc=Vm sin(wt)   [Math. 1]MathFigure 2Ax=A sin(wt)+n(t)   [Math. 2]MathFigure 3Bx=B sin(wt)+n(t)   [Math. 3]
In Math Figures 1 to 3, Vm, A, and B represent constants, respectively.
In Math Figures 2 and 3, n(t) represents common mode noise (noise−>n(t)).
A first multiplier 12 of the signal processor 10 outputs a signal Ax·Bx obtained by multiplying the first voltage Ax of the first receiver coil 6 by the second voltage Bx of the second receiver coil 8, and the signal Ax·Bx can be expressed by the following Math Figure 4.MathFigure 4Ax·Bx=AB sin2(wt)+(A+B)sin(wt)·n(t)+n2(t)   [Math. 4]
Since sin2(wt) is expressed by the following Math Figure 5 according to a trigonometric function equation, the above Math Figure 4 can be expressed by the following Math Figure 6.
                                              ⁢                  MathFigure          ⁢                                          ⁢          5                                                                                              ⁢                                            sin              2                        ⁡                          (              wt              )                                =                                    1              -                              cos                ⁡                                  (                                      2                    ⁢                                                                                  ⁢                    wt                                    )                                                      2                                              [                  Math          .                                          ⁢          5                ]                                                          ⁢                  MathFigure          ⁢                                          ⁢          6                                                                              Ax          ·          Bx                =                                            AB              ⁡                              (                                  1                  -                                      cos                    ⁡                                          (                                              2                        ⁢                                                                                                  ⁢                        wt                                            )                                                                      )                                      2                    +                                    (                              A                +                B                            )                        ⁢            sin            ⁢                                                  ⁢                                          (                wt                )                            ·                              n                ⁡                                  (                  t                  )                                                              +                                    n              2                        ⁡                          (              t              )                                                          [                  Math          .                                          ⁢          6                ]            
When the signal obtained by Math Figure 6 is passed through a first low pass filter 14, all cos(2wt) and sin(wt) components are removed, and thus the above Math Figure 6 can be expressed by the following Math Figure 7.
                    MathFigure        ⁢                                  ⁢        7                                                                      Ax          ·          Bx                =                              AB            2                    +          N                                    [                  Math          .                                          ⁢          7                ]            
In Math Figure 7, N is not 0 (N≠0) and is represented as N=GLPF (n2(t)), and GLPF represents the transfer function of the low pass filter (LPF).
In the same manner, a second multiplier 13 of the signal processor 10 outputs a signal B·Bx obtained by multiplying the second voltage Ax of the second receiver coil 8 by itself, and when the signal is passed through a second low pass filter 15, all cos(2wt) and sin(wt) components are removed, which can be expressed by the following Math Figure 8.
                    MathFigure        ⁢                                  ⁢        8                                                                      Bx          ·          Bx                =                                            B              2                        2                    +          N                                    [                  Math          .                                          ⁢          8                ]            
A divider 16 of the signal processor 10 outputs a value obtained by dividing the value obtained by the first multiplier 12 by the value obtained by the second multiplier 13, and the output value can be expressed by the following Math Figure 9.
                    MathFigure        ⁢                                  ⁢        9                                                                                  Ax            ·            Bx                                Bx            ·            Bx                          =                              AB            +                          2              ⁢                                                          ⁢              N                                                          B              2                        +                          2              ⁢                                                          ⁢              N                                                          [                  Math          .                                          ⁢          9                ]            
In the signal processor 10, a third multiplier 18 obtains a final output value Vout by multiplying the value obtained by the above Math Figure 9 by a reference voltage Vref.
Therefore, in the case of the conventional inductive angle sensor, the common mode noise is not removed even when a ratio-metric is used in the signal processor 10 in the above manner, and thus the common mode noise rejection such as electromagnetic compatibility (EMC) characteristic is low.
While the first receiver coil 6 has a structure in which the differential signal varies when the coupler 4 rotates, the second receiver coil 8 has a structure in which the differential signal varies according to a change in distance from the coupler 4 regardless of the rotation of the coupler 4, and thus the shape and operational characteristics of the first and second receiver coils 6 and 8 are different from each other. Moreover, since the first and second receiver coils 6 and 8 do not vary in the same direction with respect to a change in voltage generated by the exciting coil 2 and induced noise, the change in voltage or the noise is not removed even when the divider 16 is used by the ratio-metric method.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.